The Big Gun Cannon

So you want to know about Big Gun cannons. You know they shoot big steel balls, have multiple barrels, and make quite a bang (splash!) when they shoot. But you don't quite know how they work, or what's so special about them. Well you've come to the right place, because this topic is all about the design, construction, and operation of the Big Gun cannon.

At the heart of every cannon ever designed is the Simple Pressure Cannon Design. The SPCD is the most basic mathematic model for calculating performance of a cannon, and the closer a cannon design is to the SPCD, the better it will be. It is very simple: on one side of the projectile, you have a pressure source. On the other side, you have the barrel. It looks something like this:

PRESSURE--->ball---->barrel

The pressure applies a force to the projectile, accelerating it down the barrel until it leaves the cannon. Note that this only works for "ideal" cannons, that do not suffer physical limitations such as non-ideal gasses, friction, blow-by, and other ailments. For pressurized gas cannons, another element is necessary, the firing valve. The firing valve prevents the pressurized gas from moving the projectile until the cannon is ready to fire. Also, there is no pressure source that can provide constant-pressure gas throughout the entire firing sequence, the closest a real-world cannon can get to that is a pressure-storing tank called an accumulator. So the SPCD for pressurized-gas cannons looks like this:

Accumulator--->valve--->ball--->barrel


As you can see, pressurized gas stored in the accumulator is released when the valve is opened, which then pushes the ball down the barrel and towards the target. As the ball travels down the barrel, the gas expands and pressure drops. The larger the accumulator, the smaller the pressure drop-off.

This model can be applied to both Big Gun and Fast Gun cannons. For Fast Gun cannons, the accumulator is the volume of pipe between the magazine and O-ring, and the o-ring itself is the valve. Upon pulling the trigger, the accumulator is charged up until there is sufficient pressure to open the valve (by forcing the ball through the o-ring)and then the built-up gas pushes the ball down the barrel. In Big Gun cannons, the accumulator is kept charged at all times until the trigger is pulled, opening the valve and allowing the stored gas to push the ball out the barrel.

Here is where we find the fundamental difference between Big Gun and Fast Gun cannons. When you want to fire a Fast Gun cannon, you charge it up and it will fire upon reaching its set pressure (adjustable via "tweaking" the o-ring), whereas Big Gun cannons are charged at all times, and firing merely opens the valve. This allows Big Gun cannons to be powered by an air compressor, which may take several seconds to fully charge the cannon. In fact, Big Gun cannons were originally invented for air compressors, and freon (later CO2) was introduced several years later. The delay caused by air compressors charging accumulators eventually formed the basis for rate of fire limitations in Big Gun combat.

Before we take a look at the first cannon, there are a few terms we must define.

1) Accumulator: The accumulator is a volume chamber that stores pressurized gas for firing.
2) Valve: The valve is the "trigger" of the cannon. Open the valve and the cannon fires. The most common valve is a large poppet valve, commonly mislabeled the "ball valve" as shorthand for the more accurate term "buna ball valve". Although these buna ball valves are most common, other valves such as quick exhaust valves may be used.
3) Bearing: The bearing is the part that the cannon rotates on. it is usually a large-diameter ball bearing, although other bearings can be used.
4) Breech: The place were the magazine feeds balls into the barrel in preparation for firing. The breech also includes a selector mechanism to fire only one ball per barrel, and comes in closed and open versions.
5) magazine: the place where ammunition is stored before it is fired. Usually an open tray, although tubes are also used.
6) Barrel Riser: The vertical tube that leads from the breech to the barrels. Some cannons without barrel depression use a single pipe as both barrel riser and barrel.
7) Barrel: The horizontal tube that points the ball in the right direction upon firing.
8) Actuator: The "finger that pulls the trigger". The Actuator is the component that, when pressurized, opens the valve to fire the cannon.

Familiarize yourself with these terms, because I will be using them a lot to describe the various big gun cannons.

 

Now that we know the basics of how a cannon operates, let's take a look at the simplest of Big Gun cannons, the MJV-2 or "Arizona" gun.

The Arizona gun is a simple single-barrel cannon that can be built to fire several sizes of shot. It can be modified to rotate, or it can be daisy-chained together to get multiple barrels in a single turret. The main identifying components are a MAT-2 or homemade accumulator, an MJV-2 valve, and an MPA-3 actuator. Here's a picture:


This particular example was taken from the stern of a Deutschland pocket battleship. It features three Arizona guns chained together to fire at the same time, and feed from a single large rectangular tray-style magazine. The accumulator for each barrel is a Clippard MAT-2 volume tank, and its identifying feature is the MJV-2 valve that the other components are attached to. The breech for each barrel was ordered from a custom brass plumbing company to work secifically with 7/32" diameter balls.

When the fire command is given, a pulse of air travels into the MPA-3 actuators, which open each MJV-2 valve. The MJV-2 valves vent the gas from the accumulator into the breech, where the gas pushes the loaded ball up and out. As the loaded ball travels up, it pushes the next ball in the breech back up and into the magazine, which prevents the next ball from loading until after the cannon is done firing. The loaded ball then travels up the barrel, through the bend, and then out towards the target.

The Arizona cannon's strength lies in its use of the MJV-2 valve. MJV-2 valves are designed for use in industry, and as such are far more reliable than other valves, and also requires less manufacturing on the part of the cannon builder. An Arizona cannon can be built with a drill press, barrel bender, and hand tools. Its weakness is that it is difficult to rotate and depress. They are best used in large numbers on maneuverable boats, or as a single-barrel defense cannon on armed transports.

more coming soon, be patient

 

Moving this one to "how to" section

 

You asked, so here ya go!

Here we have a pretty standard Arizona BB cannon. This particular model was a single-barrel design (not intended to be daisy-chained together) for use in the bow of a light cruiser. To save length, the accumulator has been rotated 90 degrees, and it was made of soldered and polished copper pipe so it could fit in the narrow bow portion of the ship it was intended for. It does not have a barrel or tube magazine yet, but everything else is exactly as shown in the pictures.


This shows the cannon minus its MPA-3 firing actuator. As you can see, all the actuator does is press a button on the larger MJV valve. I would have also removed the accumulator, but it is currently sealed and I'd rather not reseal it again.


And here we have it, the inside of the breech. The T fitting has two 1/4" compression threaded inputs and one 1/8" NPT threaded input. To the right of that is the single-shot selector piston. When the cannon fires, air rushes up beneath this piston and pushes it up, closing the breech and both preventing additional balls from firing and air from leaking into the magazine. When the trigger is released and pressure drops, the piston drops back down to its original position and allows another ball to be loaded. Note that this is not spring-loaded because the cannon is only allowed to fire once every two to four seconds, depending on the club. Lastly we have a small spacer. This particular cannon was made with an MJV-3 valve rather than the usual MJV-2, and the spacer was required to set the piston so that it would load only one ball, instead of two.

 

Before I move on to other cannon designs, we need to go over the most common breech mechanism in Big Gun cannons. In my previous post about Arizona guns, the sample cannon used a moving piston to close the breech. However, the majority of Big Gun cannons do not use a moving piston. In fact, the standard breech has no moving parts whatsoever (asides from the ammunition). This type of breech, when named at all, is called motionless breech or solid-state breech.

The basic operating procedure is to have the loaded ball suspended slightly beneath the ammunition in the magazine. This allows the next ball in line to overlap slightly above the loaded ball. When the cannon fires, the loaded ball must push the next ball in line out of the way and back up the magazine before it can continue through the barrel and towards its target. This causes all the balls in the magazine to roll away from the breech for the split second it takes to fire the cannon, preventing more than one ball from firing at any one time. When properly constructed, the solid-state breech will provide reliable single-shot action for many years without maintenance. However, if improperly tuned, the cannon may fire two balls, a spurt, or no balls at all.

Methods for positioning the loaded ball include sleeving down the breech beneath the ball, using a horizontal pin to prevent the ball from dropping, or (when possible) threading a small screw up from beneath for adjustable positioning of the ball.

 

Carl, do you have any plans for a closed breech gun with rotation and depression? It would seem that this type wouldn't be as wasteful "gas wise" helping reduse the freezing of regs in fast firing conditions.

 

Mark, it depends on how many barrels and what caliber you want. Yes, there is a cannon firing four 1/4" steel balls, closed-breech with rotation and depression. It is called the Stomper because of the unique way in which its entire magazine drops down to close the breech and fire in the same motion. There are also only two working samples in the entire world due to the extreme complexity of manufacture, and I still don't fully understand its internal workings. On the other hand, its a fairly simple matter to make a single-barrel Arizona cannon rotate and depress. The design to use depends on what its being used for, and what the builder is capable of. Some cannons are very tall and don't fit in all ships, others require lots of precision machining.

Can you be a little more specific about what you're looking for? I plan to cover every Big Gun cannon design that I know of, but if there's one that would suit your needs then I can cover it sooner rather than later.

 

is there a web site that shows tese cannons??

 

There is no comprehensive, detailed website showing how each of these cannons. There is some information scattered about the web, so I can provide you the links.

The North Texas group has a backup of the old South Coast Battle Group's technical articles, which has some notes about Arizona guns and ball valves for Indiana guns:
http://www.ntxbg.org/pgOnTheWays/SCBG_Tech/articles_list.htm

The Queens Own club in 1/72 scale has some stuff about Arizona Guns, including rotation. Note that some of their techniques do not work in 1/144 scale:
http://www.queensown.org/armament/gun-construction.html
http://www.queensown.org/armament/armament.html

 

Carl, go to this website and look at the diagram shown of the gun
http://www.rcwarships.com/rcwarships/bb44/sarmament.html
this is the type I'm interested in, I'll show it to some of the guys from my dive team (they have a nice machine shop they use for their car projects) and see if we can duplicate it, but if you have any iput on these guns I'd appreitiate it.

 

did you get a chance to look at that site yet?

 

Yes, I saw. That is a very interesting design, in that the action of closing the breech also fires the cannon. As such, it is classified as a "sliding breech" gun. Sliding breech guns, including the one you linked to, are very gas-efficient. They can also be chained together fairly easily to fire several barrels at once from the same component, or even chained together to fire 10 or more barrels from a single assembled cannon. The downside is that they are difficult to rotate. At the bottom of the page, the author specifically mentions that two separate units would be mounted on a rotating platform to represent a twin 5" gun, so no rotation was ever planned.

I am working on the diagrams for the Indiana cannon, and I hope to post that soon. Since the Indiana cannon is the one to which all others are compared, I think its best to get that posted before I do any more comparing.

 

Thanks for the input. So really is there any difference between sliding breech and closed? I'm going to need gas efficient guns for the 3rd's to help with freezing issues. How about using this type (modified to fire several balls)for torps?

 

Copies of the original J.C. White plans for what has since come to be called the "Indiana" cannon are available from BDE. I got a set from Taubman as well, years ago - I don't know if he still carries them or not. There have been many improvements since those plans were drawn, but nothing that changes the basics of how they work.

JM

 

have you looked at using green gas? It may help with your freezing issue Mark.

 

o

 

it would be funny to see a ship blow up.